1. Field of the Invention
This invention relates to a new adsorbent for use in selective adsorption of carbon monoxide and unsaturated hydrocarbons, the manufacture of the adsorbent and a separating process employing the same. More specifically, this invention relates to an adsorbent having a high degree of selectivity and affinity for both carbon monoxide molecules and unsaturated hydrocarbon molecules and also having highly improved adsorptive capacity for carbon monoxide and unsaturated hydrocarbons, and a process for producing the same. More specifically, this invention relates to a CO and/or unsaturated hydrocarbon separation process employing a specially prepared adsorbent to effectively separate CO and/or unsaturated hydrocarbons from a mixed gas containing CO and/or unsaturated hydrocarbons together with a component selected from the group consisting of H.sub.2, N.sub.2, Ar, He, CH.sub.4, C.sub.2 H.sub.6, C.sub.3 H.sub.8, CO.sub.2, and mixtures thereof, in an efficient manner using an adsorbent having a high adsorptive capacity for CO and unsaturated hydrocarbons.
2. The Prior Art
Carbon monoxide and unsaturated hydrocarbons are basic raw materials in synthetic chemistry. In industry, the problem of separating carbon monoxide satisfactorily from mixed gases has not been solved so far. On the other hand, carbon monoxide and/or unsaturated hydrocarbons present in some raw material gases as harmful impurities are required to be removed. For instance, in ammonia plants, an ammoniacal solution of cuprous carbonate or formate has been employed for removal of carbon monoxide for many years. However, this purification process has certain shortcomings including a difficulty in controlling the operation for the prevention of the formation of precipitates, corrosion of the equipment, loss of the solution and high construction costs due to use of high pressures.
In the 1970's, the Tenneco Co. employed a toluene solution of copper(I) aluminium tetrachloride (Cu(AlCl.sub.4)) as an absorbing medium, which could selectively absorb carbon monoxide or ethylene from a mixed gas (U.S. Pat. No. 3,651,159 (1972); CHEMTECH, May, 1975, p.308-311; Oil and Gas Journal, No. 52 Vol. 76 Dec. 25(1978)). The medium could absorb 1.6 m mol of CO per ml at 30.degree. C. and 578 mm Hg of partial pressure of CO, but would lose its absorptive ability irreversibly when contacting with water. Moreover, the resulting hydrogen chloride from the hydrolysis of the medium when contacting with water would corrode the equipment involved, and the precipitates formed in the process would block up the pipes. For these reasons, the feed gas must be pretreated by zeolite adsorption to reduce its water content to less than 1 ppm. Besides, the toluene used as the solvent would volatile into the collected carbon monoxide during desorbing, which made it necessary to further separate and recover the solvent by an adsorption step with activated carbon.
In order to overcome the shortcomings in using the liquid form absorbing medium, solid form adsorbents have been proposed. In U.S. Pat. No. 4,019,879, copper(I) zeolites have been employed to separate carbon monoxide from gas streams. The Cu(I) zeolite is prepared by ion-exchange between a zeolite and a solution of cuprous salt in a non-aqueous solvent or by reduction of a Cu(II) zeolite. But its adsorptive capacity for carbon monoxide is low. It could only adsorb about 2% CO by weight of the adsorbent.
In recent years, Hirai et al. have prepared a CO adsorbent by impregnating active carbon with a toluene solution of copper(I) aluminum tetrachloride, or by steeping active carbon in a hydrochloric acid solution of cuprous chloride, and then removing the solvent by heating or pumping (U.K. Pat. No. 2,117,265A). The adsorbent can adsorb about 1 m mol of CO or ethylene per gram of the adsorbent at 20.degree. C. and 0.9 atm of partial pressure of CO.
The adsorptive capacity for carbon monoxide or ethylene of any of the solid form adsorbents mentioned above is lower than that of the toluene solution of copper(I) aluminium tetrachloride.